High voltage coaxial switch and associated apparatus



N Jan. 31,1967 F. M. coLLlNs ETAL. 3,301,983

HIGH VOLTAGE COAXIAL SWITCH AND ASSOCIATED Al''lURTUS Filed Aug. 27, 1964 NQM i 5 F uw m w M am R 0 f W QQ w\vm m E Nm Q W M m w 7 V L T S L m M W u u @QTQQ R, l j mm M M scL Q mmf mm N, T 0 wmv m F nl R S w O M wm\ w m E w L P W F. mWTP c H mw vl A M A E w a f I 1 F N R m N\ Y Qm, Y S ww B 5 WYIMJAQWI mw uw Y N m Qm vm mv vv mw mv i Nam l n U mm um mm mm BY'BUCKHORN, HLORE, KLROU/ST 8 SPAR/(MAA ATTORNEYS 3,301,983 HIGH VOLTAGE COAXIAL SWITCH AND ASSOCIATED APPARATUS Frank M. Collins, McMinnville, and .lack R. Hipperson,

McMinnville, Greg., by Nina May Hipperson, adminstratrix for estate of .lack R. Hipperson, deceasedaassignors to Field Emission Corporation, McMinnville, Greg., a corporation of Oregon Filed Aug. 27, 1964, Ser. No. 392,558 6 Claims. (Cl. 20G-153) The subject matter of the present invention relates generally to electrical switches, and in particular to a coaxial switch and associated apparatus for transmitting narrow, high voltage pulses of short rise time. Briefly, the present coaxial switch includes a movable contact which can be reciprocated between a signal output position where it is connected to an output transmission line, 4and a dummy load position where it is in contact with a liquid load resistor which dissipates the energy of the high voltage pulse. A flexible insulator member of oil-filled silicone rubber is employed as a connector seal between the switch and the end of an input transmission line and/ or between such switch and an output transmission line. This flexible insulator prevents voltage Abreakdown along the surface of a solid insulator between the inner and outer conductors of the external transmission line and of a section of coaxial transmission line within such switch. A capacitive voltage divider is formed by a conductor ring supported coaxially within the outer shield conductor and around the inner signal conductor of the input transmission line which provides a tirst capacitor between such inner conductor and such ring, and a second capacitor 'between such outer conductor and such ring to produce a monitor signal across the second capacitor which is similar to an input signal transmitted through such line.

The switch structure of the present invention may be employed in any apparatus which transmits high frequency signals or pulses of short rise time, and is especially useful in the pulse generator system shown in copending U.S. patent application Serial No. 400,392, filed September 30, 1964, 'by Robert L. Anderson et al. and entitled High Voltage Storage Module, Pulse Generator and System. This pulse generator system may be used to supply pulses of high voltage and high current to exploding wires in order to heat such wires to an extremely high temperature before causing them to explode. When the switch structure of the present invention is employed in this manner, it operates as a discharge directive switch which determines the path of the high Voltage pulse to cause such pulse to ow either to a signal output terminal connected to the'exploding wires, or to a dummy load in the form of a liquid resistor contained within the switch structure.

The switch structure of the present invention has several advantages over conventional switches, including a coaxial construction so that the switch forms a short section of transmission line having substantially uniform characteristic impedance which prevents signal reflections within the switch that would distort the output signal of such switch. 'The present switch may be actuated automatically by means of a Huid cylinder whose piston rod is connected to the movable contact of the switch by energizing a solenoid valve connected to such cylinder. The liquid load resistor employed inthe present switch apparatus has an advantage over lconventional load resistors in that it is smaller in size, dissipates .heat faster, and is capable of handling pulses of high energy without lbeing destroyed. ',The capacitive voltage divider of thel present invention has anadvantage over conventional monitoring apparatus dueto itslsimple coaxial structure which prevents any appreciable signal reflection from such voltage divider. Such voltage divider is also extremely efficient in extract- 'United States Patent O ice ing a portion of the input signal applied to the switch without attenuating such signal appreciably. Another advantage of the capacitance voltage divider is its extreme accuracy because of the precise value of the output capacitor formed by a pair of conductors coated on the opposite sides of a strip of plastic insulating material to maintain the distance between such conductors substantially uniform.

The flexible insulator and connector seal member in the present switch structure has several advantages over conventional rigid insulators because it conforms to the surfaces of the insulators at the ends of the switch and the device 'being connected to such switch to prevent the existence of any air interface at such surfaces which might cause voltage breakdown. In addition, the oil-filled flexible insulator and connector of the present invention has an advantage over conventional all-liquid insulators, such as oil, in that it is much easier and less troublesome to insert and remove.

It is, therefore, one object of the present invention to provide an improved high voltage switch structure of simple and economical construction.

Another object of the present invention is to provide an improved switch structure for transmitting high frequency signals in which the switch forms a section of coaxial transmission line of substantially uniform characteristic impedance to prevent any appreciable signal reilections within such switch structure.

A further object of the invention is to provide an improved coaxial switch structure in which the movable contact of such switch may be moved automatically between two xed output contacts to provide two different paths for signals applied to a fixed input contact of the switch.

An additional object of the present invention is to provide an improved high voltage coaxial switch structure in which a liquid resistor `is employed within such switch structure as a dummy load to dissipate electrical pulses of high energy which are applied to the switch, in one position of a movable contact of such switch.

Another object of the invention is to provide an improved liquid resistor of small size and a hollow, cylindrical shape which does not change its effective resistance for high frequency signals due to a skin effect or high voltage gradients.

Still another object of the invention is to provide a' therewith to prevent voltage Ibreakdown along the surface of such rigid insulator.

Other objects and advantages of the present invention will be apparent from the detailed description of a preferred embodiment thereof, and from the attached drawings, of which:

FIG. l is a partial section view of a high voltage switch structure made in accordance with the preferred embodiment of the present invention;

FIG. 2 is a vertical section view taken along the line 2 2 of FIG. l; and

FIG. 3 is an enlarged View of a ratus of FIG. l showing the details of the capacitance voltage divider.

As shown in FIG. l, one embodiment of the switch structure of the present' invention includes a tubular housing member lil formed in a T-s-hape by a pair of intersecting hollow circular cylindrical portions. An annular portion of the appa-- input conductor rod 12 forming one fixed contact of the switch is mounted within the Ihousing extending coaxially with respect to one of the cylindrical portions and is supported by a solid insulating spacer 14 of epoxy resin or other suitable insulative material, which is bonded to the inner surface of the housing and to the outer surface of the input conductor. An annular output conductor rod 16 forming another xed switch contact is mounted coaxially Wit-hin one end of the other cylindrical portion of the housing by means of another insulating spacer 18 similar to spacer `14. The movable contact of the switch structure is in the form of a cylindrical plunger 2t) which is provided with la conical recess 22 in one end thereof for engagement with the tapered end of output conductor rod 16 in the switch position shown in FIG. 1, in order to connect such output conductor to input conductor 12.

The other end of plunger is threaded onto a connecting shaft 24 of insulating material, such as nylon, which is connected to a piston rod 26 for movement with a piston 28 mounted wit-hin fluid operated cylinder 30. The cylinder 30 may be connected by tubes 32 and 34 `attached to the opposite ends thereof to a source of compressed air, nitrogen or other gas, or to a source of oil or other liquid through a solenoid actuated valve 36. The valve 36 is energized by transmitting electrical current through lead wires 38 to cause gas to ow into cylinder 30 through line 32 in order to move the piston 28 and the plunger switch contact 20 to the right into the position shown. When it is desired to move the plunger to the left, the solenoid valve 36 is actuated so that gas flows through line 34 into the cylinder 30 `and forces the piston 28 into the position shown in dashed lines. This causes the vfrustoconical end of plunger 20 attached to connecting shaft 24, to engage a complementary shaped metal terminal member 40 on one end of a dummy load resistor, so that such terminal member forms the second fixed output contact of the switch.

The load resistor is formed by a pair of concentric, hollow envelope cylinders 42 and 44 of epoxy resin plastic, glass or other dielectric which have their righthand ends attached to the outer and inner edges, respectively, of the annular terminal member 4i) and have their lefthand ends attached to a second terminal member 46. Thus, members 40, 42, 44 and 46 form `a closed uid tight envelope which contains a liquid resistance material 48, such as an aqueous solution of copper sulphate (CuSO4) or silvernitrate (AgNOB), or some other chemical salt solution. When copper sulphate is employed as the resistance liquid 48, the terminal members 40 and 46 are formed of copper, and when the resistance liquid is silver nitrate the end terminals are fonmed of silver, in order to prevent a change in resistance of the liquid due to a chemical reaction of such liquid with the metal of the end terminals. Thus, the liquid resistance material 48 provides a hollow, cylindrical load resistor having a resistivity between l0 and 100 ohms per centimeter, depending upon the concentration of the resistance solution, which may withstand pulses of extremely high volt age up to about 300 kilovolts yper inch. The effective resistance of such liquid resistor does not change appreciably for high frequency signals due to the skin effect.

The end terminal 46 of the liquid resistor is attached to and insulated from a mounting plate 5t) in any suitable manner, such as by nylon screws, and a thin layer 52 of plastic tape, which may `be polyethylene tei-ephthalate sold by E. I. du Pont de Nemours and Co. under the trademark Mylar, so that such end terminal is not at the ground potential of the housing 10. The mounting plate Si) is attached to an end plate 54 of the switch structure by means of bolts 56 and such end plate is secured to the opposite end of housing 1u from output conductor 16 by means of other bolts 58. The plunger shaft 24 slides within the inner envelope cylinder 44 of the liquid resistor through apertures in end terminals 40 and 46 and also through apertures in support plate 50 and end plate 54. The interior of the housing 10 is provided with a filling of dielectric fluid, such as oil, so that a fluid-tight seal (not shown) must be provided between the plunger shaft and the wall of the aperture in either end plate 54 or support plate 50 in any suitable manner, such as by providing a rubber O-ring in an annular slot surrounding such aperture.

The input conductor 12 is provided with a hollow switch contact portion 60 at one end thereof and such contact portion has a cylindrical passageway 62 therethrough of slightly greater diameter than plunger 20. The input conductor 12 is supported so that the passageway 62 extends coaxially wit-h the plunger 20, resistor 48 .and output conductor 16 to enable the reciprocation of suoh plunger within such passageway to form a connection between the input conductor and such output conductor or between such input conductor and liquid resistor 48. A pair of Vhelical coil springs 64 are positioned within a pair of spaced annular notches provided in the inner surface of the passageway 62 in contact with portion 60 so that such springs engage the plunger 20 and provide a good electrical connection `between such plunger and the input conductor y12. In the switch position shown, the input conductor 12, the plunger 20 and the output conductor 16 form the inner conductor of a section of coaxial transmission line whose outer conductor is formed by housing 16, and which has a substantially uniform characteristic impedance of 60 ohms.

When the plunger 20 is unged to the left into the position shown hy dashed lines, current flows from the input conductor 12 through such plunger to the input terminal 40 of the liquid resistor and then through the liquid resistance material 48 to the output terminal 46 of such resistor. The output terminal 46 of the liquid resistor is connected through a current viewing resistor 66 such as model SGR-l-OS produced by T & M Research Products of Albuquerque, New Mexico of lower value than such liquid resistor, to ground by a threaded terminal pin 68 which extends through an oversized hole in support plate S0 and is threaded into a recess in terminal member 46. The output end of the current viewing resistor is connected through a leafspring type coaxial cable connector 70 to the input of a cathode ray oscilloscope or other monitoring instrument for observing the waveform and amplitude of the current pulse transmitted through the dummy load resistor and the current viewing resistor 56. It should be noted that the viewing resistor 66- is grounded Iby a support clamp 72 attached to such resistor to the end Iplate 54 through which the resistor extends. The output terminal 46 of the liquid resistor is insulated from the ground potential of mountin-g plate 50* by the plastic layer S2.

As stated above, the interior of the switch housing 16 may be filled with 4insulating oil or gas by means of a fluid connector 74 through a hole in the side of the casing and such connector is shut off after the casing is filled with oil. A second fluid connector '76 may also be provided `on the housing and such connector is coupled to a tluid accumulator 78 having a flexible diaphragm 80 therein to separate the oil from air or other gas in such accumulator. The accumulator maintains the pressure of the oil within the housing substantially constant regardless of the changes in volume of such oil due to the movement of plunger 20 and temperature variationsl which would otherwise increase in pressure and mi-ght shatter the envelope portions 42 and 44- of the liquid resistor or Ibreak the switch housing.

In order to prevent voltage breakdown between the housing 10 and the inner conductors 12 and 16 along the surface of spacer members 14 and 18, such spacer members are each provided with a plurality of concentric annular grooves 82 and `84, respectively, on the end surfaces in communication with the oil llinzg in the housing to provide an elongated path for surface creep. Surface creep type of voltage breakdown is also prevented at the surfaces on the other side of the spacers 14 and 18 by providing a flexible insulator and connector seal member 86 in contact with such surfaces.

The flexible insulator and connector seal member 86 may be made of a resilient plastic material such as synthetic silicone rubber material sold by the General Electric Company under their trademark Silastic and identification RTV-882. The silicone rubber may be mixed with the proper amount of la silicone oil, such as that sold by Dow Corning Inc. u-nder their number D.C. 200, to render the insulator member sufficiently ilexible and provide better electrical insulation. The exible insulator me-mber 86 is molded in an annular double reentrant shape having a pair of frustocon-ical end portions which merge into an annular ridge at the bases of such end portions. The insulator member is provided with a pair of inwardly extending cavities at the opposite ends thereof which are joined by a smaller passageway 88 of circular cross section that extends axially.

In order to connect the input conductor 12 of the switch lstructure to a pulse generator (not shown), the output conductor 90 attached to such pulse generator is inserted through the passageway 88 in insulator member 86 and into a recess in the end of such input conductor opposite from plunger receiving portion 60. The recess in the input conductor may be provided with an annular notch for holding a coil spring 92 which -maintains inner conductors 12 and 90 in good electrical contact. The outer conductor casing 94 of the pulse generator is bolted onto t-he housing of the switch by means of bolts 96 extending through threaded holes in outwardly extending iianges t-hereon. A rigid spacer 98 of epoxy resin, or other suitable plastic, is provided inside casing 94 to support the inner conductor 90l coaxially within the outer conductor portion of such casing and such spacer is provided with an elongated reentrant surface to increase the path of voltage creep. When the bolts 96 are tightened, the flexible insulator member 86 is squeezed between t'he insulating spacers 14 and 98 so that such flexible member flows into `all portions of the void between such spacers. In addition to the oil filling within the tiexible insulator member 86', such insulator member is dipped in oil to wet the entire surface of the insulator member. This coating of oil prevents any air interface from existing along the mating surfaces of such insulator member and the spacers 14 and 98 to further prevent voltage breakdown between the inner conductors 12 and 90 and the outer conductors 10y and 94.

It should be noted that .the syntheic silicone rubber of the ilexible connector and insulator member 86 is substantially incompressible and will be slightly extruded out between the housing flanges as the bolts 96 are tightened. Too much extrusion is undesirable because the extruded plastic would prevent good electrical contact between such anges and would not give the best mechanically rigid connection. In any event, the iiexible insulator member is not porous and does not act in the manner of a sponge to hold the oil within interior cavities. Therefore, it is possible to merely apply the oil to the surface of the molded insulator member 86 and get similar insulation results. However, when such oil is mixed homogeneously with the silicone rubber, such oil enters into the chemical reaction of the cure of such rubber and renders the rubber more flexible. For this reason it is desirable to mix the oil with such rubber before molding. The dielectric constants of the synthetic rubber and oil of the flexible insulator member do not exactly match that of the epoxy resin in spacers 14 and 98 so that there is some nonuniformity in the characteristic impedance of the coaxial transmission line formed by the inner conductor of members 12 and 90 and the outer conductor of members 10 and 94. However, this discontinuity does not cause any appreciable signal distortion, and it is possible to compensate for this change in dielectric con# stant by tapering the inner conductor to provide a transmission line having a substantially uniform characteristic impedance.

In order to obtain a monitor signal from a portion of the high voltage input signal transmitted through output conductor 90 to the switch, a capacitance voltage divider is provided by positioning a ring electrode 100 within the casing 94 of the pulse generator coaxially with respect to the inner conductor 90. The ring electrode 100 is insulatingly spaced from the outer conductor in a manner hereafter described with respect to FIG. 3, a shorter distance than it is spaced from they inner conductor in order to provide a greater capacitance C2 between such ring electrode and the outer conductor. The ring electrode is connected by a terminal lead 102 through a hole in the side of casing 94 to a coupling resistor 104 which is connected to an output terminal 106 through the inner conductor of a short section of coaxial cable 107 whose outer conductor is grounded. The output end of the coaxial cable is terminated in its characteristic impedance by a resistor 108 connected between the inner conductor of such cable and ground. Thus, the coupling resistor 104 and the coaxial cable 107 may be provided by a passive electrical probe which is connected to the ring electrode 100 of the capacitance voltage divider.

As shown in FIG. 3, the ring electrode 100 may be provided as a copper coating of .002 inch thickness on one side of a strip 110 of plastic, such as polytetrafluoroethylene sold under the trademark Teflon, of .005 inch thickness which may have a second copper coating 112 on the opposite side thereof. Since the thickness of the plastic strip 110 is extremely uniform, the capacitance C2 between the two copper coatings 100 and 112 is very accurate and may be about 5000 picofarads. The coated plastic strip 110 is positioned so that the copper coating 112 is in electrical contact with the outer conductor housing 94 and may be fastened by conductive epoxy resin to the housing in that position. Thus, the capacitance C2 between the ring electrode and the coating electrode 112 is also the capacitance between such ring electrode and outer conductor 94. The capacitance C1 between the ring electrode 100 and the inner conductor 90 of the transmission line may be on the order of 5 picofarads when the transmission line has the dimensions to provide a line having a characteristic impedance of about 60 ohms. Thus, the input signal voltage Vm is applied across both capacitors C1 and C2 connected in series, while the moni-y tor output voltage is obtained across the capacitor C2 through the resistive divider formed by resistors R1 and R2. Since V2, the voltage produced across the capacitor C2, is equal to V2 is approximately equal to 1/ 1000 of Vm, due to the fact that C2 of 5000 picofarads is very large compared to C1 of 5 picofarads. When the coupling resistor R1 equals 1125 ohms and the characteristic impedance of the cable is ohms so R2 equals 125 ohms, the output voltage Vont transmitted to output terminal 106 is R2 RVi-R2 Vin X gether or may be left open without affecting the Voperation of the capacitance voltage divider. Also the sides of the metal coatings 100 and 112 maybe etched back from the edges of the plastic strip 110 to prevent voltage breakdown between such coatings due to surface creep. The capacitance voltage divider of the present invention provides an extremely efficient way of monitoring a high voltage signal of short rise time without causing any appreciable signal distortion and without attenuating the signal by any great amount. This is due to the coaxial construction of such voltage divider which reduces the amount of signal reiiected therefrom.

It will be obvious to those having ordinary skill in the art that various changes may be made in the details of the above-described preferred embodiment of the present invention without departing from the spirit of the invention. For example, the ri-ng electrode 100 may be positioned adjacent the spacer 14 to provide a capacitive voltage divider within the switch housing 10. Therefore, the scope of the present invention should only be determined by the following claims.

We claim:

1. A switch structure, comprising:

a hollow housing member having a tubular first outer conductor portion and a tubular second outer conductor portion whose axis intersects that of said first portion;

a first inner conductor mounted coaxially within said first portion of said housing member and insulatively spaced from said housing member, said first inner conductor having a cylindrical passageway extending through one end of said first inner conductor coaxially with said second portion of said housing member;

a second inner conductor mounted coaxially within said second portion insulatively spaced from said housing member and spaced from said rst inner conductor; and

a movable switch contact member mounted for sliding movement within said passageway of said first inner conductor into and out of engagement with said second inner c-onductor to selectively connect said second inner conductor in electrical contact with said first inner conductor, said passageway surrounding said switch contact member and guiding the movement of the switch contact member to maintain said switch contact member coaxial with said second conductor and insulatingly spaced from said housing.v

2. A coaxial f transmission line comprising: v

a hollow housing member having a pair Iof coaxial tubular output portions and a tubular input portion extending laterally to the axis of said output portions;

an inner input conductor mounted coaxially within said input portion of said housing member and insulatively spaced from said housing member, said input conductor having a cylindrical passageway extending through one end of said input conductor coaxially within said output portions of said housing member;

- a pair of rst and second inner output conductors mounted coaxially within different ones of said output portions and insulatively spaced from said housing member, said output conductors being spaced from said input conductor;

a movable switch contact member mounted coaxially within said output portions for longitudinal sliding movement within said passageway of said input conductor, said passageway surrounding said switch contact member .and guiding the movement of the switch contact member to maintain said switch contact member coaxial with said second conductor and insulatingly spaced from said housing; and

actuating means attached to one end of the switch contact member and extending through one of said switch structure,

output portions to the exterior of said housing, for moving said `switch contact member into engagement with said first output conductor in a first switch position and for moving said switch contact member into engagement with said second output conductor in a second switch position.

3. A high voltage coaxial transmission line switch,

comprising:

a hollow housing member having a pair of coaxial tubular output portions and a tubular input portion extending laterally to the axis of said output portions;

an inner input conductor -mounted coaxially within said input portion of said housing member and having a cylindrical passageway extending through one end of said input conductor coaxially with said output portions of said housing member;

a first annular spacer of insulating material supported between said input conductor and said housing member;

an inner output conductor mounted coaxially within one of said output portions spaced from said input conductor;

a second annular spacer of insulating material supported between said output conductor and said housing member;

a filling of dielectric liquid within said housing; and

a movable switch contact member mounted coaxially within said fluid inside the other of said output portions for axial sliding movement within said passageway of said input conductor into and out of engagement with said output conductor while maintaining electrical contact with said inner conductor, said passageway surounding said switch contact member and guiding the movement of the switch contact member to maintain said switch contact member coaxial with said second conductor and insulatingly spaced from said housing.

4. A coaxial transmission line switch, comprising:

a hollow housing member having a pair of coaxial tubular output portions and a tubular input portion extending substantially perpendicular to the axis of `said output portions;

an inner input yconductor mounted coaxially within said input portion of said housing mem-ber and insulatively spaced from said housing member, said input conductor having al cylindrical passageway extending through one end'of said input conductor coaxially with said output portions of said housing member;

an inner output conductor mounter coaxially within one of said output portions insulatively spaced from said housing member spaced from Said input conductor;

a filling of dielectric liquid within said housing member; i f

a movable switch contact member mounted coaxially within said liquid inside the other of said output portions for sliding movement within said passageway of said input conductor while maintaining electrical contact with said inner conductor, said passageway surrounding said switch contact member and guiding the movement of the switch contact member to maintain said switch contact member coaxial with said second conductor and insulatingly spaced from said housing;

iiuid cylinder means outside said housing member for moving said switch contact member into engagement with said output conductor in a iirst switch position and for moving said switch contact member out of engagement with said output conductor in a second switch position; and

means for maintaining the pressure of the dielectric liquid substantially constant.

5. An electrical discharge directive switch, comprising:

a hollow housing member having a pair of coaxial tubular 4output portions and a tubular input portion extending substantially perpendicular to the axis of said output portidns;

an inner input conductor mounted coaxially within said input portion of said housing member and insulatively spaced from said housing member, said input conductor having a passageway extending through one end of said input conductor coaxially within said output portions of said housing member;

an inner output conductor mounted coaxially within one of said output portions insulatively spaced from said housing member and spaced from said input conductor;

a dummy load resistor mounted coaxially within the other of said output portions of said housing member, said resistor having an aperture extending therethrough;

a movable switch contact means including a plunger member mounted coaxially within said output portions for sliding movement within said passageway of said input conductor while maintaining electrical contact with said inner conductor, and `a plunger shaft extending through the aperture in said resistor and connected to Said plunger member; and

means to automatically reciprocate the plunger shaft for moving said plunger member into engagement with said output conductor in a rst switch position and for moving said plunger member out of engagement with said output conductor and into contact with said load resistor in a second switch position.

6 An electrical discharge directive switch, comprising:

a hollow housing member -having a pair of coaxial tubular output portions and a tubular input portion extending laterally to said output portions;

an inner input conductor mounted coaxially within said input portion of said housing member and insulatively spaced from said housing member, said input conductor having a passageway extending through one end of said input conductor coaxially with said output portions of said housing member;

an inner output conductor mounted coaxially within one of said ou-tput portions insulatively spaced from said housing member and spaced from said input conductor;

a dummy load resistor including an envelope containing liquid resistance material coaxially mounted within the other of said output portions of said housing member;

a movable switch contact member mounted coaxially within the other of said output portions for sliding movement Within said passageway of said input conductor while maintaining electrical Contact with said inner conductor; and

means including a fluid operated cylinder and piston,

for moving said switch Contact member into engagement with said output conductor in a rst switch position, and for moving said switch contact member out of engagement with said output conductor and into engagement with an end terminal of said resistor in a second switch position.

References Cited by the Examiner UNITED STATES PATENTS 2,614,243 10/1952 Clark 323-77 2,639,310 5/1953 Hun-t 174-30 2,662,142 12/1953 Nelson 200-153 2,671,153 3/1954 Ray et al. 338-80 2,771,529 11/1956 Kostriza 200-153 2,826,746 3/1958 Lanctot 200-153 X 2,899,482 8/1959 Stevens 174-30 2,932,786 4/ 1960 Kohn et al. 323-77 3,115,613 12/1963 Evans 338-80 FOREIGN PATENTS 791,123 2/1958 Great Britain.

ROBERT K. SCHAEFER, Primary Examiner.

H. HOHAUSER, Examiner. 

1. A SWITCH STRUCTURE, COMPRISING: A HOLLOW HOUSING MEMBER HAVING A TUBULAR FIRST OUTER CONDUCTOR PORTION AND A TUBULAR SECOND OUTER CONDUCTOR PORTION WHOSE AXIS INTERSECTS THAT OF SAID FIRST PORTION; A FIRST INNER CONDUCTOR MOUNTED COAXIALLY WITHIN SAID FIRST PORTION OF SAID HOUSING MEMBER AND INSULATIVELY SPACED FROM SAID HOUSING MEMBER, SAID FIRST INNER CONDUCTOR HAVING A CYLINDRICAL PASSAGEWAY EXTENDING THROUGH ONE END OF SAID FIRST INNER CONDUCTOR COAXIALLY WITH SAID SECOND PORTION OF SAID HOUSING MEMBER; A SECOND INNER CONDUCTOR MOUNTED COAXIALLY WITHIN SAID SECOND PORTION INSULATIVELY SPACED FROM SAID HOUSING MEMBER AND SPACED FROM SAID FIRST INNER CONDUCTOR; AND A MOVABLE SWITCH CONTACT MEMBER MOUNTED FOR SLIDING MOVEMENT WITHIN SAID PASSAGEWAY OF SAID FIRST INNER CONDUCTOR INTO AND OUT OF ENGAGEMENT WITH SAID SECOND INNER CONDUCTOR TO SELECTIVELY CONNECT 